docs: def _prune_fields(field_dict, only):
          """Filter fields data **in place** with `only` list.
  
          Example::
  
              self._prune_fields(field_dict, ['slug', 'text'])
              self._prune_fields(field_dict, [MyModel.slug])
          """
          fields = [(isinstance(f, str) and f or f.name) for f in only]
          for f in list(field_dict.keys()):
              if f not in fields:
                  field_dict.pop(f)
          return field_dict